JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    <ul id="main">
    <li class="list" style="background-color:#fed">
        <h2>To do <em>(2)</em></h2>
        <ul class="tasks">
            <li class="task">Drink coffee</li>
            <li class="task">Go to work</li>
        </ul>
    </li>
    <li class="list" style="background-color:#edf">
        <h2>Doing <em>(4)</em></h2>
        <ul class="tasks">
            <li class="task">Get dressed</li>
            <li class="task">Read the newspaper</li>
            <li class="task">Send a text message to mom</li>
            <li class="task">Fix world hunger</li>
        </ul>
    </li>
    <li class="list" style="background-color:#dfe">
        <h2>Done <em>(3)</em></h2>
        <ul class="tasks">
            <li class="task">Wake up</li>
            <li class="task">Select clothes to wear for important meeting</li>
            <li class="task">Put on some deodorant</li>
        </ul>
    </li>
</ul>

CSS

html, body, #main {
    margin: 0;
    padding: 0;
    overflow: hidden;
    display: block;
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    right: 0;
}

#main {
    display: flex;
    overflow-x: auto;
    overflow-y: hidden;
    font-family: 'Cambria';
    white-space: nowrap;
}

ul, li {
    display: flex;
    flex-wrap: nowrap;
    justify-content: flex-start;
    list-style: none none inside;
    margin: 5px;
    padding: 5px;
}

.group, .list, .task {
    box-shadow: rgba(0, 0, 0, 0.5) 0 2px 3px;
    border-radius: 5px;
}

.group, .list, .tasks {
    flex-direction: column;
}

.list {
    flex-grow: 1;
    flex-wrap: nowrap;
}

h1, h2 {
    flex-grow: 0;
    margin: 0;
    padding: 0;
}

h1 {
    font-size: 21px;
}

h2 {
    font-size: 16px;
}

.tasks {
    flex-wrap: wrap;
    flex-grow: 1;
}

.task {
    background-color: #f3f3f3;
    width: 250px;
    white-space: normal;
    cursor: move;
}

.task:hover {
    background-color: #fff;
}